Vaccines can have non-targeted or heterologous (also called non-specific) immunological effects on the immune system i.e. effects other than inducing an immune response against the disease targeted by the vaccine. This trial aims to evaluate the non-specific immunological effects of two vaccines - diphtheria-tetanus-acellular pertussis (DTP) vaccine and seasonal influenza vaccine - in a cohort of elderly humans (>65 years of age) and healthy adult control subjects (30-50 years).